KR100252798B1 - Water-based coating compositions and their use for the coatings - Google Patents

Abstract

Heat-crosslinkable, aqueous coating compositions which contain, as binder, a combination of a) a water-soluble or -dispersible polyol component with b) a water-soluble or -dispersible polyisocyanate component containing blocked isocyanate groups, made from b1) a polyisocyanate mixture having a mean NCO functionality of from 2.5 to 3.5 comprising (i) at least 15% by weight of a diisocyanate component and (ii) tri- and/or higher-functional polyisocyanates, b2) blocking agents for isocyanate groups, and b3) at least one aliphatic monohydroxycarboxylic acid, and optionally conventional auxiliaries and additives, and the use thereof for coating metallic substrates with stoving finishes (baking finishes).

Description

Water-Based Coating Compositions and Their Uses for the Preparation of Flexible Coatings

The present invention relates to a novel water based coating composition for the production of stoving lacquers, more specifically for the production of elastic fillers for the coating of car bodies.

Recently, lacquer and coating compositions based on water have become increasingly important in view of the increasingly stringent release criteria for solvents flowing out during coating. While water based coating compositions have been developed for a variety of applications, high quality solvent containing coating compositions have not been obtained in terms of solvent and chemical resistance, elasticity (flexibility) and mechanical stability. More particularly, elastic fillers for the coating of car bodies are still coated from liquids, which meet the stringent practical requirements required to meet impact strength, resistance to chipping and resistance to water and chemicals. There is no coating composition based on polyurethane.

It is disclosed in British Patent No. 1,444,933 on hydrophilic modification of aromatic polyisocyanates, European Patent Publication No. 0,061,628 and German Patent Publication No. 2,359,613, German Patent Publication No. 4,001,783 on certain anionic modified aliphatic polyisocyanates, and blocked polyisocyanates And German Patent Publication Nos. 2,456,469, 2,814,815, European Patent Nos. 0,012,348 and 0,424,697 for binders based on organic polyhydroxyl compounds for water-based stoving lacquers. Carboxy-functional polyurethane prepolymers containing blocked isocyanate groups according to German Patent Publication No. 2,708,611 and highly functional blocked water soluble urethane prepolymers according to No. 3,234,590 are almost unsuitable for the production of flexible coatings.

If selected combinations of the above-mentioned types of water-soluble or water-dispersible polyhydroxyl compounds a) containing a specific water-soluble or water-dispersible blocked polyisocyanate component b) are used as binders, they can be coated from a liquid and the above requirements It has been found by the present invention that a stoving filler can be produced that meets this requirement.

The present invention

a) a water soluble or water dispersible polyol component, and

b) from 2.0 to 2.6, based on isocyanate groups that contain blocked isocyanate groups, the average NCO functionality being reversibly blocked,

b1) a polyisocyanate mixture having an average NCO functionality of 2.5 to 3.5, (i) at least 15% by weight of a diisocyanate component containing at least one organic diisocyanate and (ii) an average NCO functionality of 2.5 to 3.5, b1) Polyisocyanate mixtures containing a polyisocyanate component containing at least one trifunctional or at least trifunctional polyisocyanate in an amount sufficient to produce

b2) at least one reversible monofunctional blocking agent for isocyanate groups, which is present in an amount of from 50 to 80 equivalent percent based on the isocyanate groups of component b1), and

b3) a reaction product of at least one aliphatic monohydroxymonocarboxylic acid, present in an amount of 20 to 50 equivalents based on the isocyanate group of component b1) and the hydroxyl group of component b3), the reaction product being Converted to salt form at least partially by neutralization of the incorporated carboxyl groups, the equivalent ratio of component b1) to isocyanate groups being at least 0.9: 1 based on the isocyanate group reactive groups of blocking agent b2) and the hydroxyl groups of component b3) Or to a thermally crosslinkable water based coating composition containing a binder comprising a water dispersible polyisocyanate component.

The invention also relates to a metal substrate coated with the coating composition.

The binder component a) is selected from water-soluble or water dispersible polyhydroxyl compounds of average molecular weight (calculated from Mn, hydroxyl group content and hydroxyl functionality) of 1,000 to 100,000, preferably 2,000 to 10,000. Such polyhydroxyl compounds are known in the polyurethane coating art and are poly-containing sufficient amounts of hydrophilic groups, more particularly ethylene oxide units and / or carboxylate groups, to allow the polyhydroxyl compounds to dissolve or disperse in water. It should contain ether chains. However, it is also possible to use polyhydroxyl compounds which do not have sufficient hydrophilicity in themselves in mixtures with external emulsifiers.

Component a) is selected from known polyhydroxy polyesters, polyhydroxy polyethers and other hydroxy functional polymers such as polyhydroxy polyacrylates. The polyol has a hydroxyl number of 20 to 200, preferably 50 to 130, based on the solids.

Polyhydroxyl polyacrylates are known copolymers of styrene with esters of acrylic acid and / or methacrylic acid. Hydroxyalkyl esters (eg, 2-hydroxyethyl, 2-hydroxypropyl and 2-, 3- or 4-hydroxybutyl esters of these acids) are used to introduce hydroxyl groups.

Suitable polyether polyols are known ethoxylated and / or propoxy of suitable 2- to 4-functional starting molecules such as water, ethylene glycol, propanediol, trimethylol propane, glycerol and / or pentaerythritol. Misfired product.

Examples of suitable polyester polyols are known reaction products of polyhydric alcohols such as the alkane polyols described above with excess polycarboxylic or polycarboxylic anhydrides, preferably dicarboxylic or dicarboxylic anhydrides. . Suitable polycarboxylic acids or polycarboxylic anhydrides are diels- with adipic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride, maleic acid, maleic anhydride, their cyclopentadiene Diels-Alder adducts, fumaric acid and dimers or trimer fatty acids. Mixtures of polyhydric alcohols and mixtures of acids and anhydrides can also be used in the preparation of polyester polyols.

Polyester polyols are described in Houben-Weyl, Methoden der organischen Chemie, Vol, XIV, G. Thieme-Verlag, Stuttgart, 1963, pp. 1-4].

Hydrophilic modification of the polyhydroxyl compound is carried out by known methods, for example, by methods described in European Patent Publication No. 0,157,291 or European Patent Publication No. 0,427,028 (US Pat. No. 5,126,393, incorporated by reference herein). do. Particularly suitable are the water soluble or water dispersible urethane modified polyesters described in the preceding publications. The water soluble or water dispersible hydroxy functional polymers described in German Patent Publication No. 3,829,587 (US Pat. No. 5,075,370 incorporated herein by reference) are also suitable as component a) according to the invention.

The choice of the polyisocyanate component b) is an important feature of the present invention. Polyisocyanate component b) contains water-soluble or water-dispersible blocked isocyanates having an NCO functionality of 2.0 to 2.6 based on blocked polyisocyanate groups. The polyisocyanate component b) is suitable for diisocyanate and trifunctionality, since the required opposing properties, for example good elasticity and high crosslink density, ie resistance to water and chemicals, can only be achieved by this method. It is important to be based on the specific polyisocyanate mixture b1) in which all (or) trifunctional or higher polyisocyanates are present.

The polyisocyanate mixtures b1) used for the production of component b) have an average NCO functionality of 2.5 to 3.5 and provide at least 15% by weight of the diisocyanate component and the required NCO functionality containing at least one organic diisocyanate. A polyisocyanate component containing at least one trifunctional or trifunctional or higher polyisocyanate in an amount sufficient for.

Suitable diisocyanates are 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (IPDI) or 4, 4'-diisocyanatodicyclohexyl methane. Difunctional derivatives of hexamethylene diisocyanate (HDI), for example uretdione diisocyanates corresponding to formula (I) with an organic HDI content of preferably less than 0.5% by weight, are also components according to the invention. It is suitable as a diisocyanate component of b1).

Such uretdione diisocyanates are disclosed in German Patent Publication Nos. 1,670,720, 3,437,635, 3,432,081, 3,809,261 (US Pat. No. 5,043,092, incorporated herein by reference) and 3,900,053 ( Prepared by oligomerization of hexamethylene diisocyanate by known methods described in US Pat. No. 4,994,451, which is incorporated herein by reference. In addition to dimerization products containing uretdione groups, relatively high functional trimerization products containing isocyanurate groups are also generally produced during oligomerization reactions such that the average functionality of the oligomerization products is from 2.0 to 2.7. . When oligomerization products of this type are used, the percentage of tri- and tri- or higher polyisocyanates already present should be taken into account in the calculation of the average NCO functionality of the mixture b1).

Suitable trifunctional and trifunctional or higher polyisocyanates are known and include trifunctional or higher polyisocyanates containing isocyanate groups which are bonded aromaticly but preferably (cyclo) aliphatic. Especially suitable are urethanes, allophanates, biurets and, in particular, derivatives of hexamethylene diisocyanate containing isocyanate groups, containing less than 0.2% by weight of free hexamethylene diisocyanate and having an average NCO functionality of 3 to 6.

In a particularly preferred embodiment, the higher functional polyisocyanates are hexamethylene diisocyanate derivatives containing isocyanurate groups, containing less than 0.2% by weight free hexamethylene diisocyanate and having an average NCO functionality of 3.8 to 4.2. .

Starting mixture b1) generally has an NCO content of about 15 to 30% by weight. To prepare the polyisocyanate component b) 50 to 80% of the isocyanate groups of the starting mixture b1) are blocked by the blocking agent b2) by known methods and 20 to 50% of the isocyanate groups are reacted with the monohydroxycarboxylic acid b3). do. The reaction with the two components can be carried out in any order. The only requirement for the reaction is 1) the equivalent ratio of the isocyanate reactive groups of the blocking agent b2) and the hydroxyl groups of the component b3) to the isocyanate groups of the component b1) is at least 0.9: 1, and 2) the number of isocyanate groups of b1) When less than the sum of the isocyanate-reactive groups of b2) and the hydroxy groups of b3), monohydroxycarboxylic acid b3) is first reacted with a total amount of blocking agent b2) to react all hydroxyl groups of component b3) One or more isocyanate groups are allowed to react. It is also possible to use isocyanate groups of component b1) or isocyanate reactive groups of blocking agent b2) in a slight excess. Thus, the equivalent ratio is at least 0.9: 1, preferably from 0.95: 1 to 1.1: 1.

Suitable monofunctional blocking agents are known and are epsilon caprolactam, malonic acid diethylester, acetoacetic acid ethyl ester and oximes such as butanone oxime. Butanone oxime is a preferred blocking agent.

Suitable hydrocarboxylic acids b3) are 2-hydroxyacetic acid, 3-hydroxypropanoic acid or 12-hydroxy-9-octadecanoic acid (ricinoleic acid). Preferred carboxylic acids are those in which the carboxyl group is disturbed by its steric effect on its reactivity. Particular preference is given to 3-hydroxy-2,2-dimethyl propanoic acid (hydroxypivalic acid).

In order to produce the polyisocyanate component b), the starting mixture b1) is reacted continuously or simultaneously with the blocking agent b2) and the hydroxycarboxylic acid b3) in any order. In a preferred embodiment, a portion of the blocking agent is first It is reacted with hydroxycarboxylic acid and then with the remaining blocking agent. In this embodiment, some excess blocking agent may be used. However, the reaction can also continue if a few unreacted NCO groups still remain in the reaction mixture. The reaction is generally carried out at 0 ° C to 120 ° C, preferably 20 ° C to 60 ° C. In particular, hydroxycarboxylic acid b3) is reacted under mild conditions to prevent the reaction of NCO and carboxyl groups.

The reaction is carried out without solvent or in an inert solvent which can optionally be removed after distillation, neutralization and water after the reaction. Suitable solvents are those which are not reactive with NCO groups, for example ketones such as acetone and methyl ethyl ketone, esters such as ethyl acetate and also N which may remain in the coating composition in small amounts to perform stabilization and flow control functions. Solvents such as -methyl pyrrolidone.

Upon completion of the reaction, at least a portion of the incorporated carboxyl groups is neutralized with a suitable neutralizer. Suitable neutralizing agents include alkali metal or alkaline earth metal hydroxides, but t-amines such as triethylamine, triethanolamine and, in particular, N-dimethyl ethanolamine are preferred. In general, at least 80% of the carboxyl groups present are neutralized and neutralizing agents may be used in excess. Component b) preferably contains 60 to 130 milliequivalents of carboxylate groups per 100 g of solid.

After neutralization, water is preferably added in an amount such that 20 to 50% by weight of an aqueous solution or dispersion of component b) is formed. If a low boiling point solvent is used in the preparation of the polyisocyanate component b), this solvent can be removed from the water phase, for example by vacuum distillation. As noted above, high boiling point solvents such as N-methyl pyrrolidone may remain in the coating composition in small amounts (less than 10% by weight). They act as flow regulators and stabilizing aids.

In another embodiment, polyisocyanates b), optionally containing free carboxyl groups and blocked isocyanate groups in the form of an organic solution, can be mixed with an aqueous solution of neutralizing agent to neutralize and dissolve or disperse in one step to obtain an aqueous solution or dispersion.

In order to prepare the coating composition according to the invention, an aqueous solution or dispersion of polyhydroxyl component a) is preferably added to an aqueous solution or dispersion of blocked polyisocyanate b) and preferably to an alcoholic hydroxyl group of component a). Mixing is such that the equivalent ratio of blocked isocyanate groups of component b) to 0.6: 1 to 1.5: 1, more preferably 0.7: 1 to 1: 1. Although less preferred, it is also possible to mix an aqueous solution or dispersion of polyhydroxyl component a) with a neutralizing agent and optionally with an unneutralized blocked polyisocyanate b) in the form of an organic solution.

Known additives such as pigments, flow regulators, antifoams, catalysts and also other binders (e.g. melamine / formaldehyde or urea / formaldehyde resins) in water-based binder mixtures or individual components a) or b) Can be added prior to mixing.

The coating composition according to the invention can be coated on the heat resistant substrate in one or more layers by known methods, for example spray coating, electrodeposition coating, dip coating, flood coating or coating by rollers and coating knives. Can be.

Coatings on metals, plastics, wood or glass are obtained, for example, by curing the coatings at 80 to 220 ° C, preferably at 130 to 180 ° C.

The coating composition according to the invention is particularly suitable for the production of lacquer finishes and for the preparation of coatings on metal plates of the type used for the production of, for example, bodies, machines, linings, containers and containers and the like. These are preferably used for the production of automotive fillers. Lacquer films generally have a dry layer of 0.01 to 0.3 mm thick.

The binder according to the invention provides durable surface protection as illustrated in the examples below. High chipping resistance is particularly emphasized, which makes it very suitable for binders to be used in applications requiring high chipping resistance.

A particular advantage of the novel water based binder is that it is stable even when stored at room temperature and some elevated temperatures between 30 and 60 ° C. Another advantage of the novel water based binders is that they are easily processed and can be easily regenerated by ultrafiltration.

In the examples below, all parts and percentages are by weight unless otherwise noted.

EXAMPLE

Example 1 Preparation and Description of Starting Materials

1.1. 4,4'-diisocyanatodicyclohexyl methane (product of Tesmodur W. Bayer AG), NCO functionality 2.0

1.2. Oligomerization Product of 1,6-Diisocyanatehexane, NCO Functionality 2.3

2,000 g of 1,6-diisocyanatohexane were placed in a suitable reaction vessel and heated to 50 ° C. 20 g of 2,2,4-trimethylpentane-1,3-diol and 30 g of tri-n-butyl phosphine were added by stirring in a nitrogen atmosphere. Exothermic reaction was maintained at 60 degreeC by cooling. After 6 hours of reaction, the NCO content of the reaction mixture was 42.5%. 16.5 g of toluene sulfonic acid methyl ester was added to stop the reaction and heated to 80 ° C. for 2 hours. The crude product was separated from excess starting diisocyanate in downstream evaporator (165 ° C./l millibar) and thin layer evaporator (150 ° C./0.30 millibar).

The properties of the isolated product are as follows.

NCO Content (%) 21.6

Viscosity (mPa.s / 23 ° C) 200

Hazen Singa 50

Free starting diisocyanate (%) 0.2

NCO sensory about 2.3

Gel chromatography analysis showed that 72% of the oligomerization product is uretdione diisocyanate of formula (I) and the remainder is tris- (6-isocyanatohexyl) -isocyanurate, its higher homologues, urethaneization products And high homologues of uretdione diisocyanate.

1.3. Oligomerization Product of 1,6-Diisocyanatohexane with NCO Functionality 3.9

Thin isocyanurate polyisocyanates were prepared from 1,6-diisocyanatohexane according to Example 1 of European Patent Publication No. 0,010,589 (US Pat. No. 4,324,879) (NCO content 21.5%, viscosity 2,100 mPa.s (25 ° C.), monomeric 1,6-diisocyanatohexane content of 0.1% and triisocyanatohexyl monoisocyanurate content of about 49%). The remainder was a mixture of high molecular weight homologs containing 2 or more isocyanurate groups per molecule. The average NCO functionality was about 3.9.

Example 2 Preparation of Polyisocyanate Component b) Dissolved in Water

Ingredients: 97.5 g of polyisocyanate of Example 1.3

65.5 g of polyisocyanate of Example 1.1

Butanone Oxime 56.6g

27.5 g of hydroxypivalic acid

Dimethyl aminoethanol (DMAE) 29.7 g

N-methyl pyrrolidone (NMP) 15.4 g

325.0 g of water

Reaction method

34.8 g of the first portion of butanone oxime was added to a mixture of two polyisocyanates (average functionality: about 2.6) while cooling to below 80 ° C. at a rate not exceeding 80 ° C. After cooling to 50-60 ° C., NMP and hydroxypivalic acid were added. The mixture was slowly heated to 90-100 ° C. The initial reaction was slightly exothermic. After 5-8 hours at this temperature the reaction was stopped when the NCO content was determined to be 4.3-4.6% by dibutyl amine titration. The remaining amount of butanone oxime 21.8g was added slowly, and the mixture was stirred gently at 90 ° C. until the NCO content was measured by IR and became zero. The mixture was neutralized with DMAE. After 10 minutes, the reaction mixture was dispersed in 325 g of water heated from 80-90 ° C. to 60-70 ° C. A clear solution having a solid content of 40% and a viscosity of 25,000 mPa · s (23 ° C.) was obtained. The blocked isocyanate content in the solution was 4.4%. Functionality based on blocked NCO was 2.03.

Example 3- Preparation of Polyisocyanate Components Dissolved in Water

Component: 146.3 g of polyisocyanate of Example 1.3

48.8 g of polyisocyanate of Example 1.2

Butanone Oxime 56.6g

27.5 g of hydroxypivalic acid

Dimethyl aminoethanol (DMAE) 31.2 g

NMP 17.5 g

370.0 g of water

Reaction method

34.8 g of the first portion of butanone oxime was added to a mixture of two polyisocyanates (average functionality: about 3.3) with cooling below 80 ° C. at a rate not exceeding 80 ° C. After cooling to 50-60 ° C., NMP and hydroxypivalic acid were added. The mixture was slowly heated to 90-100 ° C. The initial reaction was slightly exothermic. The reaction was stopped after 3-5 hours at this temperature when the NCO content was determined to be 3.5-3.8% by dibutyl amine titration. After 21.8 g of the remaining butanone oxime was slowly added, the mixture was stirred gently at 90 ° C. until the NCO content was determined by IR to zero. The mixture was neutralized with DMAE. After 10 minutes, the reaction mixture was dispersed in 370 g of water heated from 80 to 90 ° C to 60 to 70 ° C. A clear solution having a solid content of 40% and a viscosity of 30,000 mPa · s (23 ° C.) was obtained. The blocked isocyanate content in the solution was 3.9%. The sensory degree based on blocked NCO was 2.55.

Example 4 Hydroxy Functional Urethaneized Polyester Resin Based on Water

509 g of peanut oil fatty acid, 1,051 g of hexane-1,6-diol, 560 g of cyclohexane-1,4-dimethanol, 1,093 g of adipic acid, 1,243 g of isophthalic acid and 940 g of trimethylol propane were agitated, heated and cooled, and water It was placed in a 10 l reaction vessel equipped with a separator and esterified at 220 ° C. until the acid value was 5 or less.

3540 g of the polyester and 330 g of dimethylol propionic acid were dissolved in 700 g of N-methyl pyrrolidone and 10 g of dibutyl tin oxide were added, and the resulting solution was reacted with 1,000 g of isophorone diisocyanate at 70 ° C. The reaction continued at 70-110 ° C. until no more NCO groups were detected. After adding 135 g of methyl diethanolamine, the resin was dispersed in 5,100 g of water. About 45% resin solution was obtained. The organic solvent content was 6.5%. The content of the reactive hydroxyl group bonded to the polyester resin was 1.17%.

Example 5 Water-Based, hydroxyl-functional Urethaneized Polyester Resins

361 g of benzoic acid, 2,316 g of trimethylol propane, 2,853 g of hexane-1,6-diol, 1,602 g of cyclohexane-1,4-dimethanol, 3,130 g of adipic acid, 2,931 g of isophthalic acid and dimer fatty acids (prepol 1,008, Unikema Co., Ltd.) 300 g was placed in a 15 L reaction vessel equipped with a stirrer, a heating and cooling device, and a water separator, and esterified at 210 ° C until the acid value was 3 or less.

1,020 g of the polyester and dimethyl 87 g of propionic acid were dissolved in 2,000 g of acetone at 60 ° C. After addition of 1.5 g of dibutyl tin dilaurate as catalyst, 230 g of isophorone diisocyanate, 65 g of 4,4'-diisocyanatodicyclohexyl methane were added and the mixture at 60 ° C. until free NCO groups were no longer detected. Was stirred. After adding 35 g of dimethyl ethanolamine and 1,600 g of water, acetone was removed by distillation. About 45% resin solution without organic solvent was obtained. The content of isocyanate-reactive hydroxyl groups in the solution was 1%.

Example 6 Preparation of Filler Resin of Aqueous Blocked Isocyanate and Aqueous Hydroxide Component

22.0 parts of the water based resin of Example 4 and 21.6 parts of the water based resin of Example 5 were thoroughly mixed with 19.3 parts of the aqueous polyisocyanate of Example 3. The blocked NCO: OH equivalence ratio was 0.7. 15 parts of titanium dioxide (rutile), 0.2 parts of iron oxide black, 4.8 parts of heavy spar, and 2.1 parts of talcum were dispersed in the mixture over 30 minutes at 2,800 rpm in a bead mill. 0.45 parts of Additol XW 395, Surfinol 104E (Surfinol 104E, commercially available surfactant additive (0.45 parts and Aerosil R 972, Aerosil R972, Germany, Vienna, Austria, respectively) 0.4 part of commercially available silicon dioxide based filler) was added together with 13.5 parts of deionized water 0.2 parts of N-dimethyl ethanolamine were added to adjust the pH value to 8.

Example 7 Preparation of Filler Resin of Aqueous Blocked Isocyanate and Aqueous Polyhydroxyl Component

The following components were mixed in a bead mill at a blocked NCO: OH equivalence ratio of 0.7 using the method described in Example 6.

22.7 parts of hydroxyl resin based on water of Example 4

22.2 parts of hydroxyl resin based on water of Example 5

17.5 parts polyisocyanate based on water of Example 2

Titanium Dioxide, Part 15.0

0.1 part of iron oxide black

4.8 parts of barium sulfate

Talcum Part 2.1

Deionized Water 13.1 Part

Additiol XW 3950.5

Surfinol104E0.5part

Aerosil R972 0.4

0.2 parts N-dimethyl ethanolamine

The pH of the paste was 8.

Comparative Example 8 Preparation of Fillers According to the Prior Art

The following ingredients were mixed and the resulting mixture was dispersed in bead mill.

26.1 parts of hydroxyl resin based on water of Example 4

25.5 parts of the hydroxyl resin of the water base of Example 5

4.4 parts of water-soluble hexamethoxymethyl melamine resins

Titanium Dioxide, Part 15.1

Iron oxide black 0.1 part

4.8 parts of barium sulfate

Talcum Part 2.1

20.2 parts deionized water

Additiol XW 395

Surfinol104E0.5part

Aerosil R 972 0.4

0.2 parts N-dimethyl ethanolamine

The pH of the paste was 8.

Example 9-Application of Resin Obtained in Examples 6, 7 and 8 as Dry Filler System

The water-based resins of Examples 6, 7, and 8 were diluted with deionized water to a viscosity indicated by a flow time of about 30 s (DIN cup, 4 mm / 23 ° C.) and subjected to cathodic electrodeposition (density, about 20 μm thick). The coated zinc phosphate steel plate coated with the applied primer was spray coated with a flow cup gun (air pressure 5 bar, relative humidity 65% / 23 ° C.).

After air drying at 23 ° C. for 10 minutes, the filler was cured for 10 minutes at 75 ° C. and 20 minutes at 165 ° C. in a recirculating air oven. The thickness of the dry film was about 35 μm.

a) a commercially available automatic surface lacquer based on alkyd / melamine resin was applied to the filler layer with a dry film thickness of about 35 μm and dried at 130 ° C. for 30 minutes, and b) the metal base coating of water based It was applied to about 20 μm, after 10 minutes it was coated with a two-component PUR clear lacquer at 80 ° C. (dry film thickness 35 μm) and dried at 130 ° C. for 30 minutes.

The test results are shown in Table 1 below. The resistant properties of the film (ie solvent, water and salt spray resistance) met the specified requirements.

Assessment Methods :

Surface lacquer quality

The gloss and appearance of the coatings on the various fillers were objectively assessed as a percentage based on the optical baseline (100 = very good, 0 = very bad).

Chipping resistant

The following test instrument was used.

a) BDA chip tester (Erichen Model 508) capable of firing 2 x 500 g steel bullets (sharp edges, 4 to 5 mm) at 23 bar air pressure at 1.5 bar

Whether the sample has a surface lacquer adhesion (1 to 3, 1 = very good surface adhesion, 3 = between the surface lacquer and filler) and the metal material is peeled off (0 to 10, 0 = no peeling off, 10 = peeling off much) Was investigated.

b) Mercedes-Benz type 490 chip tester (23 ° C and -20 ° C)

Evaluation was performed to determine surface lacquer adhesion (1 to 3) and peeling to the steel substrate up to mm ² .

TABLE 1

Table 1 shows that Examples 6 and 7 are the same as Comparative Example 8 for most of the properties tested. However, the embodiment according to the invention is certainly superior in the important properties of chipping resistance and surface hardness. Also adhesion to the surface lacquer was better in Examples 6 and 7 than in Comparative Example 8.

Although the invention has been described above for the purpose of clarity, it is for the purpose of clarity only and it is to be understood that many changes can be made by those skilled in the art without departing from the spirit and scope of the invention, except as limited by the claims of the invention. It should be understood that it is possible.

Claims (3)

a) a water soluble or water dispersible polyol component, and b) containing blocked isocyanate groups, the average NCO functionality being from 2.0 to 2.6 based on the reversibly blocked isocyanate groups, b1) a polyisocyanate mixture b1) having an average NCO functionality of 2.5 to 3.5, (i) at least 15% by weight of a diisocyanate component containing at least one organic diisocyanate and (ii) an average NCO functionality of 2.5 to 3.5 Polyisocyanate mixtures containing a polyisocyanate component containing at least one trifunctional or at least trifunctional polyisocyanate in an amount sufficient to produce, b2) at least one reversible monofunctional blocking agent for isocyanate groups, which is present in an amount of from 50 to 80 equivalent percent based on the isocyanate groups of component b1), and b3) a reaction product of at least one aliphatic monohydroxymonocarboxylic acid, present in an amount of 20 to 50 equivalents based on the isocyanate group of component b1) and the hydroxyl group of component b3), the reaction product being Converted to salt form at least partially by neutralization of the incorporated carboxyl groups, the equivalent ratio of component b1) to isocyanate groups being at least 0.9: 1 based on the isocyanate group reactive groups of blocking agent b2) and the hydroxyl groups of component b3) Or water dispersible polyisocyanate component A coating composition based on a heat crosslinkable water containing a binder consisting of. The coating composition of claim 1, wherein components a) and b) are present in an equivalent ratio of blocked isocyanate groups to hydroxyl groups in an amount corresponding to 0.6: 1 to 1.5: 1. A metal substrate coated with the coating composition of claim 1.